Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 63. (Budapest 1971)
Embey-Isztin, A.: Contribution to the mineralogy of the bauxites from Nézsa (North-Hungary)
Silicium minerals The dominant Si-mineral of the Nézsa bauxites is kaolinite. Its amount varies between 7 and 90 percent. Comparing the X-ray diffraction patterns of kaolinites in the Nézsa bauxites with those in the Transdanubian bauxites it becomes clear that the degree of crystallinity of kaolinite in the former is much higher than in the latter. The endothermic peak of the DTA-graph appears at 600 °C (Fig. 1.). According to micromineralogical investigations, small amounts of quartz, tourmaline, beryl, and a little more zircon are also present in the Nézsa bauxites. As to their origin, they are allothigenic on the basis of grain morphology. Titanium minerals On the DEBYE —SCHERRER diffractograms taken and published by earlier authors there were small traces if any of the scarce Ti-minerals (1 to 3 percent) present in the Nézsa bauxites. According to micromineralogical investigations ilmenite was believed to be the most common Ti-mineral, but lesser amounts of rutile and anatase were also proved by this method. All the rutile and anatase and some of the ilmenite was held to be epigenic. Rutilization of ilmenite was observed by J. Kiss. Our X-ray diffraction patterns demonstrate a reversed order of abundances for the Ti-minerals. Anatase is most frequent, rutile is much scarcer and ilmenite could not be identified at all. The anatase content of individual bauxite samples varies from 1.1 to 3.1 percent and the rutile content from 0.2 to 0.6 percent. Since micromineralogical investigations concern only a little part, the socalled heavy mineral fraction, of any sample, it is clear that the data about the quantity and proportions of Ti-minerals supplied by X-ray diffraction are more relevant. It is probable too that most of rutile and anatase is present in fine dispersion in grains formed during the bauxitization process. Other mineralogical constituents In one of the samples white stripes of calcite were observed. According to ils appearance, it must be a secondary mineral. The presence of gypsum and alunite could also be proved. They are presumably the decomposition products of pyrite. A relatively large amount of allothigenic chromite was also determined in the heavy-mineral fraction. Acknowledgements For taking the X-ray patterns and for valuable advice my sincere thanks are due to Dr. GY. BÁEDOSSY. Explanation of Plate I. Fig. 1. Electronmicrograph of Nézsa red bauxite. — Fig. 2. Electronmicrograph of Nézsa yellow bauxite.
